1. Field of the Invention
The present invention relates to a showerhead, and particularly, to a flat board type showerhead used in a CVD apparatus, in which gas is injected into a reaction chamber.
2. Description of the Background Art
A CVD process is very important in a method how to supply reaction gas into a reaction chamber and exhaust. The reason is because that a hydrodynamic flow of gas greatly influences to a thin film deposition. Recently, a showerhead is much used for gas injection. That is because a thin film having a good uniformity through a wide area can be obtained- by uniformly injecting gas through the wide area.
FIG. 1 is a schematic view to explain a CVD apparatus in accordance with the conventional art.
Referring to FIG. 1, a reaction chamber 10 is covered with a chamber lid 20 and provides a reaction space hermetic from the outside. An O-ring 30 is installed at an engaged portion between the chamber lid 20 and the chamber 10 so as to effectively shield the reaction space from the outside.
A slot valve 60 is installed at a lateral wall of the chamber 10. The slot valve 60 has to be opened so as to transfer a wafer 50 from a load rock chamber (not shown) into the chamber 10. A wafer supporting member 40 is installed in the chamber 10, and the wafer 50 is located on the wafer supporting member 40. The wafer supporting member 40 can be moved up and down by a transferring means 45. A heater (not shown) for heating the wafer 50 is mounted at an inner portion of the wafer supporting member 40.
A showerhead 70 is connected with a gas injection pipe 80a. The showerhead 70 is provided with a plurality of injection holes (displayed as a dotted line) at an opposite surface to the wafer 50. Gas supplied to the showerhead 70 through the gas injection pipe 80a is uniformly injected to an entire surface of the wafer 50 through the injection holes. The injected gas is exhausted through a gas exhaustion pipe 80b. 
The aforementioned CVD apparatus in accordance with the conventional art has advantages that a uniform deposition of a thin film is possible even if a diameter of the wafer 50 is large and a plasma enhanced chemical vapor deposition (PECVD) can be easily performed by using the showerhead 70 as a plasma electrode.
However, the conventional art has a disadvantage that various gas is not independently supplied through the showerhead 70. Accordingly, the CVD apparatus provided with the showerhead is mainly used as a single wafer type and has a difficulty in being applied to an atomic layer deposition (ALD) method for controlling various gas independently and supplying.